Question

The Zeroth law of thermodynamics leads to the concept of

• A. internal energy
• B. heat content
• C. pressure
• D. temperature
• E. work done

Hint:

Zeroth Law → Defines temperature
First Law → Conservation of energy
Second Law → Direction of processes (entropy)

Answer 1

The Correct Option is D

Concept: The Zeroth Law of Thermodynamics is one of the fundamental laws of thermodynamics and plays a crucial role in defining the concept of temperature. It states: “If two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.” This seemingly simple statement establishes the basis of temperature measurement and comparison.

Step 1: Understanding thermal equilibrium
Two systems are said to be in thermal equilibrium if there is no net heat flow between them when they are brought into thermal contact. This implies that both systems are at the same “thermal state.”

Step 2: Role of the third system
Consider three systems:
• System A
• System B
• System C (reference system or thermometer) If: \[ A \equiv C \quad \text{(thermal equilibrium)} \] \[ B \equiv C \] Then: \[ A \equiv B \] This establishes a transitive property of thermal equilibrium.

Step 3: Emergence of temperature concept
Because of this transitive nature, we can assign a numerical value to the thermal state of a system, called temperature. Systems in thermal equilibrium have the same temperature.

Step 4: Practical implication
This law allows the use of thermometers:
• Thermometer (System C) is placed in contact with System A → measures temperature
• Same thermometer measures System B
• If readings are equal → A and B have same temperature

Step 5: Why other options are incorrect:
• Internal energy → defined in First Law
• Heat content → related to energy transfer, not Zeroth Law
• Pressure → independent thermodynamic variable
• Work done → mechanical concept, not defined by Zeroth Law Final Conclusion: Zeroth law introduces and validates the concept of temperature.